In typical oxygen production, it is common to use one or more auxiliary vaporizers to produce oxygen at pressure, and in the case of multiple auxiliary vaporizers, complicated and expensive air boosting equipment is typical used, which adds further expense to a project.
FIG. 1 represents an embodiment of the prior art. Cooled and purified air from the adsorbers is split into two streams, with one portion going to the higher pressure (HP) column 40 for rectification, and a second portion being used as a reboiling fluid for the reboiler 23 of the auxiliary column 20, where the air is condensed before being introduced to the HP column and optionally the lower pressure (LP) column 80 via streams 6 and 8, respectively. HP column 40 and LP column 80 are thermally integrated via reboiler 41.
HP column 40 is configured to operate under conditions effective to separate the air into nitrogen and oxygen. Crude oxygen stream 42 is removed from the bottom of HP column 40, optionally cooled in auxiliary heat exchanger (not shown), reduced in pressure via a valve and introduced to a middle section of LP column 80 for separation therein.
Within HP column 40, nitrogen vapor rises towards the top and ultimately is condensed in the reboiler 41 before being reintroduced to the top of HP column 40 as liquid. Nitrogen-rich liquid 47 is then withdrawn from a top portion of HP column 40, optionally cooled in auxiliary heat exchanger (not shown), reduced in pressure via a valve, and then introduced to the top of LP column 80.
Oxygen-rich liquid 82 is withdrawn from a bottom portion of LP column 80, and pumped by second pump P2 to the reboiler that is fixed atop of HP column 40. The oxygen-rich liquid introduced to the reboiler provides the refrigeration necessary to condense the nitrogen vapor coming from HP column 40. During the course of operation, the heat provided by the nitrogen vapor causes some of the oxygen-rich liquid to vaporize. Oxygen-rich gas 44 is withdrawn from the top of the reboiler and introduced to the bottom portion of LP column 80 for further separation therein. Oxygen-rich liquid 49 is withdrawn from a bottom part of the reboiler and sent to a top portion of auxiliary column 20 for further separation therein.
Auxiliary column 20 contains a single reboiler 23 that uses a cooled and purified air stream as the reboiling fluid. This air stream is condensed within the single reboiler 23 and then combined with another air stream before one portion 6 is sent to the HP column and a second portion 8 is sent to the LP column for separation therein.
Oxygen-rich liquid accumulates in the bottom portion of auxiliary column 20 (e.g., the portion below the distillation section). As noted previously, cooled, purified air provides reboiling duty for reboiler 23, which causes some of the oxygen-rich liquid (as well as any other impurities such as nitrogen) to boil off and travel through the distillation media and ultimately withdrawn from the top of auxiliary column 20 as oxygen overheads 22 before being introduced to the bottom portion of LP column 80.
Liquid oxygen 27 is withdrawn from auxiliary column 20, pressurized to a higher pressure than the LP column (and auxiliary column) and sent to auxiliary vaporizer 30. Air coming from a booster air compressor is used as a vaporizing fluid for the vaporizer of auxiliary vaporizer 30. Gaseous oxygen is withdrawn from the top of auxiliary vaporizer 30 and collected as product.
Notably, in the embodiment shown in FIG. 1, auxiliary vaporizer 30 operates at a pressure higher than the LP column, and the auxiliary column 20 operates at a pressure substantially the same as the LP column.
In addition, the complicated separate auxiliary vaporizers and their associated piping and valves are expensive as well. This also leads to an increase in cold box volumes further raising the cost of the facility.
Therefore, it would be desirable to have an improved apparatus and method that avoids these added expenses and operates in an overall more efficient manner.